Prosecutors say he was angry about federal management of public lands and wanted to retaliate. He came under investigation after joining Nevada rancher Cliven Bundy's armed 2014 standoff over grazing fees amid hot debate over federal control of public land in the West.

Keebler's friends have said he was set up by under FBI agents who infiltrated the small group and gave him the inert device he tried to detonate near Mt. Trumbull in 2016.

A gun charge was dropped in exchange for Keebler's plea. He could face more than five years in prison when he is sentenced.